Power over Ethernet (PoE), which is outlined in IEEE Std 802.3™-2005 clause 33 (the PoE standard), refers to a technique for delivering power and data to an electronic device via a network cable, such as a twisted pair Ethernet cable. In a PoE system, power sourcing equipment (PSE) provides a power supply to electronic devices, which may be referred to as powered devices, via an Ethernet cable. PoE eliminates the need for a separate power source to deliver power to attached powered devices. Such powered devices may include voice over Internet protocol (VoIP) telephones, wireless routers, security devices, field devices to monitor process control parameters, data processors, and the like.
The PoE standard specifies a detection process for detecting a PoE powered device that is coupled to the PSE before supplying power via the Ethernet cable. To perform detection, the PSE provides a DC voltage (within a range of 2.8 to 10 Volts DC) on pairs of wires of the Ethernet cable and monitors a received current (Amps) or a received voltage (V) to detect a resistance within an expected range (approximately 25K-ohms). The PSE determines the powered device's presence using a measured Volt-Amp (VA) slope related to the powered device's voltage/current signature. If the PSE does not detect a valid resistance, the PSE does not apply power to the Ethernet port assigned to the electronic device.
In general, the PoE standard specifies a particular detection signature, which may be generated using a precision resistor. Conventional integrated circuit fabrication processes make it difficult to reliably produce an integrated resistor having a resistance with sufficient precision to provide the appropriate detection signature under potential operating conditions. When using a precise external resistor, the integrated circuit includes at least one pin to couple the integrated circuit to the external resistor. Each pin of an integrated circuit has a silicon cost, a packaging cost, and a testing cost, and unnecessary or avoidable use of a pin is undesirable. Therefore, there is a need for a reduced cost powered electronic device.